Videophone services and moving picture distribution services that use portable terminal devices in a line-switching network are coming into wide use. Services in which moving picture data received from portable terminal devices in a line-switching network or IMS (IP Multimedia Subsystem)/NGN (Next Generation Network) are stored in a server and then distributed by the server are expected to become widely popularized.
MPEG-4 (ISO/IEC 14496-2: 2003 “Information Technology Coding of Audio and Video Visual Objects—Part 2: Visual”) is widely used as a moving picture coding method in Third Generation Partnership Project (3GPP) portable terminal devices.
MPEG-4 includes intramode, in which coding uses only the image of a current frame, and intermode, in which coding is carried out by referring to the images of past frames, In intramode, input pixels are subjected to a DCT (Discrete Cosine Transform) that is carried out in units referred to as “macroblocks,” following which the DCT coefficients undergo variable-length coding. In intermode, motion compensation forecasting is carried out between input pixels and decoded pixels of past frames to find differential pixels. After the differential pixels are subjected to DCT, the motion vectors and DCT coefficients are subjected to variable-length coding.
When storing moving picture data that have been transmitted from a terminal device, the data of designated intervals in the moving picture data transmitted at real time from the terminal device are stored in a moving picture storage device (for example, refer to Patent Document 1). Because the images of previous frames cannot be referred to for the leading frame of the stored image at the time of reproduction, the leading frame must be converted to data that have been subjected to intramode coding.
FIG. 1 is a block diagram showing an example of the typical configuration of a moving picture storage system. In the moving picture storage system shown in FIG. 1, data receiver 901 receives reception data 900 from a terminal device (not shown). Reception data 900 include control data 902, which is information related to the image coding, image data 903, and audio data 904. Control data 902 and image data 903 are applied as input to image data converter 905. Image data converter 905 converts the leading frame of image data 903 that has been received to an intramode frame based on information obtained from control data 902. The image data after conversion are then supplied to switch 906. Audio data 904 are applied as input to switch 906.
When notified of the start of conversion by conversion instruction signal 909, switch 906 applies audio data 904 and image data that have undergone conversion as input to data storage unit 908 until notified of the end of conversion by conversion instruction signal 909.
However, when the moving picture storage system stores moving pictures that are transmitted from terminal devices in real time, instructions of the start and end of storage must be sent from the terminal devices to the moving picture storage system. However, the problem frequently arises that the operator of a terminal device does not recognize the method of instructing the start and end of storage.
Patent Document 1: JP-A-2002232847 (paragraphs 0002-0005, FIG. 2)